This invention relates to magnetic disc memory devices used with computers and more particularly comprises a new and improved disc pack assembly containing a single magnetic disc.
The disc pack assembly into which the present invention is incorporated is of a commonly used variety which contains a single magnetic memory disc. The disc pack assembly includes a top cover and bottom cover which together form a housing within which is mounted the single memory disc. The disc is connected to a hub, and the combination disc and hub together are permitted limited axial and radial movement within the housing. When the assembly including the bottom and top covers with the memory disc and hub are mounted on the computer with which it is used (the hub carries an armature plate which connects to the spindle drive), the hub and disc are floated in the housing so that they do not contact either of the covers, and the disc and hub can rotate freely with the drive spindle of the computer. Access to the hub by the spindle is provided through a central opening in the bottom cover, and that opening is closed by a removable cover which forms a sealed container with the top cover when mounted in place on the pack.
In accordance with prior art devices, resilient pads are incorporated into the removable cover, which extend through the opening in the bottom cover when the pack is fully assembled and engage the armature so as to hold the disc and hub in a fixed position in the housing. That arrangement, however, has proved to be not entirely satisfactory, because while the pads provide sufficient axially directed forces to prevent the disc and hub from moving axially in the housing, the pressure applied by the pads is not always sufficient to prevent lateral motion, because the resistence to lateral motion is imposed only by the frictional engagement of the pads with the armature.
In this class of disc packs, the removable cover is latched to the top cover at two diametrically opposed points, and the peripheral walls of the top and removable covers are intended to engage one another and form a seal about the entire periphery of the assembly. When the bottom cover is dimensioned so that sufficient forces are applied to prevent the lateral shifting of the disc and hub assembly in the housing, the edges of the top cover and removable cover at points intermediate the latches bow away from each other so as to open the dust seal intended to be formed at the pack periphery. The dust seal is very important to prevent contamination of the magnetic surfaces on the disc, and therefore the amount of force that can be applied to resist lateral shifting is limited if the seal is to be preserved. Thus, efforts to maximize the effectiveness of the seal and to prevent lateral displacement of the disc and hub assembly work against one another.
The resilient pads have yet another disadvantage. When the pack is clamped tightly enough so as to resist lateral shifting of the disc, the pads tend to stick to the armature, and particles of the pad are torn away when the disc moves. The particles may stick to the metal surface of the disc and adversely affect the disc performance. Various ingredients in the pads may also attack and corrode the plated metal surface. And the glue used to mount the pads is another potential source of unwanted debris.
In U.S. Pat. No. 4,194,228, a disc pack is shown which embodies a ring mounted on the top cover, to counteract some of the deficiencies of the resilient pads. The ring is not used in place of the pads, but rather is provided as a supplement to them. Because the ring is part of the top cover, it must necessarily have some clearance with the hub to allow the disc to rotate freely when mounted on the computer. Therefore, it cannot totally eliminate disc shifting. While the ring of the U.S. Pat. No. 4,194,228 may prevent the edges of the disc from crashing against the container walls, the shifting which it does permit is sufficient to allow particles to be generated due to friction within the housing. Furthermore, when the pack is subjected to large shocks to cause the disc and hub assembly to shift in the pack, albeit limited by the ring, the hub may shift slightly with respect to the disc because the disc is merely clamped to the hub and not immovably tied to it. If concentricity between the hub and disc is lost, obviously the memory disc is unusable.